It is necessary to drain air and fluid from the pleural space following operation or injury to organs within the thorax. If drainage of air and fluid from the pleural space is not sufficient, the lung will not be able to expand to fill the pleural space which may result in respiratory insufficiency or the development of infection. Many different types of drainage devices have been provided for draining the pleural space. One method of draining the pleural space is to insert a catheter into the chest with the distal end thereof sealed by a condom having the end removed, to a complicated system of up to five serially connected chambers having constricted connections. In the later systems, now the state of the art, a problem arises when there is a high volume air leak from the lung which is common in older patients with inherent lung disease. In such systems, high vacuum levels are required to remove such volumes of air. During normal respiration, a negative pressure is developed, with respect to atmospheric, in the pleural space. This is the result of the lowering of the diaphragm and the increased volume of the chest with the rise of the rib cage during inspiration. The normal value of the negative pressure is 3.5-8.0 centimeters of water. The volume flow of air is governed by the Hagen-Poiseuille Law which states that for a given pressure gradient and tube length, the determinant of flow rate is the radius of the tube. Anesthesiologists are acutely aware of this and breathing circuits in anesthesia are maintained as large and short as possible. When a tube ends in an abrupt manner in a chamber, the flow is no longer laminar but becomes turbulent which introduces added resistance to flow. The length of the tube (or pathway) is also important when vacuum is applied.
According to the formula: EQU C=12.1D.sup.3 /L
Where
D is tube diameter PA1 L is length of tubing pathway PA1 C is air flow in Liters/Minute PA1 L=2.5 ft. flow=28.9 L/min PA1 L=4.5 ft. flow=14.5 L/min PA1 L=10.0 ft. flow=7.2 L/min
For example:
Therefore, the optimum removal of air through a chest drainage device will occur when the largest tubing diameter is combined with the shortest pathway from the pleural spaced to the vacuum outlet. In addition, a minimum of abrupt changes from laminar flow to turbulent flow should interrupt the pathway.
The prior art devices do not meet these criteria. The pathway is by a series of connected chambers each of which contributes turbulence. Tubing pathways are unnecessarily long and in some cases, constrictions are utilized to control flow or pressure all of which makes a high vacuum a necessity to remove a given volume of air. Since the normal negative pressure required to keep the lung inflated and allow normal respiration is low, high vacuum negates the normal respiratory efforts. High vacuum can trap the lung against the intra pleural catheter thus occluding the catheter making the catheter ineffective and resulting in collapse of the lung. In addition, high vacuum overcomes the attempt of the lung tissue to seal itself thus causing the air leaks to continue or to increase.